It is known to provide engine cooling apparatus for cooling an engine of a motor vehicle. FIG. 1 is a schematic diagram of a known coolant circuit connected to an engine 120. The apparatus has an engine driven fluid pump 122 arranged to pump coolant through a cylinder head 120H of the engine 120 and optionally through a cylinder block 120B of the engine 120 depending on the state of a cylinder block flow valve BV. The block flow valve BV is provided at an outlet of the cylinder block 120B. The block flow valve BV is arranged to open when a temperature of a portion of the block flow valve BV exceeds a prescribed value, allowing coolant to flow through the block 120B.
A further valve (sometimes referred to as a ‘top valve’, ‘top thermostat’ or ‘top stat’) TV is provided for selectively diverting coolant that has passed through the cylinder head 120H (and cylinder block 120B if the block valve BV is open) through a radiator bypass conduit 128 and/or a radiator conduit 126C. The radiator conduit 126C is coupled to a radiator 126. The top valve TV is provided upstream of the radiator 126, directing coolant flowing out from the engine 120 down one or both of the radiator conduit 126C and bypass conduit 128.
When coolant flowing through the top valve TV is relatively cold, the coolant is directed to flow through the radiator bypass conduit 128 and not the radiator conduit 126C. Above a first (lower) critical coolant temperature, the top valve begins to ‘open’, allowing coolant to flow through the radiator conduit 126C as well as the radiator bypass conduit 128. Above a second (higher) critical coolant temperature that is greater than the first critical coolant temperature the top valve TV fully opens, closing the radiator bypass conduit 128 and directing coolant solely through the radiator conduit 126C.
It is to be understood that opening of the top valve TV and opening of the block flow valve BV is controlled by different respective actuators responsive to the temperature of coolant flowing through the respective valves TV, BV. As noted above, the block valve BV is located immediately downstream of the cylinder block 120B such that only water flowing through the block 120B can flow through the block valve BV. The top valve TV is located downstream of the block valve BV and cylinder head 120H such that coolant flowing through the cylinder head 120H or cylinder block 120B flows through the top valve TV.
The present applicant has recognised that the above described known arrangement suffers from at least two problems. Firstly, the arrangement suffers from the problem of oscillations in the state of the top valve TV as the engine warms. This is because once the temperature of coolant flowing through the bypass conduit 128 reaches the first critical coolant temperature, the top valve allows coolant to flow through the radiator 126 and the bypass conduit 128, effectively splitting the flow of coolant between the radiator 126 and bypass conduit 128. Relatively cold water from the radiator 126 therefore flows through the top valve TV, causing a drop in temperature of the top valve TV. The top valve TV responds by reducing the amount of coolant flow through the radiator 126. Frequently, the top valve TV responds by substantially stopping flow of coolant through the radiator 126. The top valve TV subsequently warms due to the flow of relatively hot coolant through the bypass conduit 128, causing the top valve TV to open again, allowing coolant to flow through the radiator 126. It is to be understood that this process of opening and closing the top valve TV may continue until the temperature of coolant flowing out from the radiator 126 has warmed sufficiently to stabilise top valve operation.
A second problem associated with the arrangement of FIG. 1 is that if the block valve BV opens whilst oscillations in coolant temperature are occurring (due to oscillation of the state of the top valve TV), the engine block 120B will be subject to coolant temperature oscillations, subjecting the block 120B to thermal shocks which may have a deleterious effect on engine performance and service life.
It is an aim of embodiments of the present invention to at least partially mitigate the disadvantages of known engine coolant systems.